A CCD vertex deetctor for a high-energy linear e+e- collider

I present a summary of the experience with CCD-based vertex detectors at the SLD experiment at SLAC, and discuss their advantages for use at a future high-energy e+e- collider. The extensive R+D programme to improve further the vertexing capabilities of CCD detectors is also outlined.Comment: 14 pages latex including 4 embedded ps files, to appear in Proceedings Vertex99 Worksho

Optical spectroscopy of a brown dwarf candidate

We have used the Low-Resolution Imaging Spectrograph on the Keck II telescope to observe the brown dwarf candidate D04 (Hawkins et al, 1998). The spectrum matches that of a spectral-type M7 dwarf, implying a photospheric temperature of $\approx 2600$K. This is consistent with the available (R-I)$_C$ and (I-K) colours. If the parallax measured by Hawkins et al is correct, then the implication is that D04 has a radius of $\sim 0.035 R_\odot$, or one-third that of Jupiter. This contradicts the predictions made by current stellar models that electron degeneracy leads to nearly constant radii for stars and brown dwarfs at masses below 0.1 M$_\odot$. We suggest that an equally valid interpretation of the data is that D04 is a VB8 analogue at a distance of $\approx 150$ parsecs.Comment: to appear in MNRAS, pink pages; 6 pages with 1 jpg, 1 postscript figur

Summary of Discussion Question 4: Energy Expandability of a Linear Collider

We report on Discussion Question 4, in Sub-group 1 (`TeV-class') of the Snowmass Working Group E3: `Experimental Approaches: Linear Colliders', which addresses the energy expandability of a linear collider. We first synthesize discussions of the energy reach of the hardware of the 500 GeV designs for TESLA and NLC/JLC. Next, we review plans for increasing the energy to 800-1000 GeV. We then look at options for expanding the energies to 1500 GeV and sketch the two-beam accelerator approach to achieving multi-TeV energies.Comment: Presented at Snowmass 2001 (6 pages, 2 figures

Probing the galactic halo with ROSAT

We discuss the current status of ROSAT shadowing observations designed to search for emission from million degree gas in the halo of the Milky Way galaxy. Preliminary results indicate that million degree halo gas is observed in the 1/4 keV band in some directions, most notably toward the Draco cloud at (l,b) = (92 deg, +38 deg), but that the halo emission is patchy and highly anisotropic. Our current understanding of this halo emission is based on a small handful of observations which have been analyzed to date. Many more observations are currently being analyzed or are scheduled for observation within the next year, and we expect our understanding of this component of the galactic halo to improve dramatically in the near future